Compounds were prepared via the
Compounds were prepared via the routes shown in , varying the sequence of reactions to install the thiazole or the phenyl ring at the end of the synthesis (pyridyl examples were prepared using similar chemistry).
The aminothiazole building blocks were prepared as shown in . 5-Aminothiazole was prepared by a Curtius rearrangement of the thiazole XEN445 and deprotection of the Boc-protected intermediate. 2-Methyl-5-aminothiazole was prepared via condensation and subsequent cyclization of aminoacetonitrile and ethyl dithioacetate. The isopropyl and cyclopropyl thiazoles were prepared in a similar fashion, after first converting the carboxylic acid to the appropriate dithioate with the Davy reagent.
Compound was screened against a diverse panel of kinases at 1μM () and found to have good general kinase selectivity, including the other class III RTKs: c-Kit, Flt3 and PDGFRβ.
Compounds with an unsubstituted thiazole (, , ) were found to have higher in vivo rat clearance than the pyridyl analogues (, , ). However, the more potent 2-methyl thiazoles also had improved PK profiles (, ). In vivo clearance could be reduced further with the introduction of fluorine on the phenyl ring (). Acceptable rat PK was also achieved when the methyl group on the thiazole ring was replaced with isopropyl ().
To assess the in vivo CSF-1R activity of the thiazolyl bisamides, compounds were dosed orally in a mouse pharmacodynamic (PD) model. 3T3 cells were engineered to express human mutant full length CSF-1R (301–969) (3T3/CSF-1R) in which the kinase activity was constitutively on. Female nude mice were implanted with 5×10 3T3/CSF-1R cells subcutaneously and grown in vivo until tumors were >250mm in size. After dosing, tumors were analyzed for pCSF-1R levels by ELISA, and blood plasma samples assessed for drug concentrations. Examples from the thiazolyl bisamide series showed excellent inhibition of pCSF-1R in vivo at 2 and 6h after dosing at 50mpk ().
Significance Preclinical data indicate that tumor-associated macrophages (TAMs) represent an attractive therapeutic target as they represent key orchestrators of various tumor-promoting processes, such as escape of immune surveillance. Here, we report that treatment with an anti-CSF-1R antibody (RG7155) depletes TAMs from the tumor tissue of cancer patients across various tumor types. Moreover, in Dt-GCT patients, a neoplastic disorder characterized by CSF-1 overexpression, RG7155-induced reduction of CSF-1Rmononuclear cells provided significant clinical benefits and offers a therapeutic option other than surgery, which is associated with a high likelihood of relapse. Furthermore, our work forms the basis for exploring combination therapies especially in those tumor entities in which TAMs contribute to tumor pathogenesis.
Introduction Colony-stimulating factor 1 (CSF-1) and its receptor, CSF-1R, regulate the migration, differentiation, and survival of macrophages and their precursors (Hume and MacDonald, 2012, Chitu and Stanley, 2006). CSF-1R is a member of the receptor protein tyrosine kinase (rPTK) family of growth factor receptors, which includes several known proto-oncogenes. The molecular pathology of the diffuse-type giant cell tumor (Dt-GCT; formerly known as pigmented villonodular synovitis [PVNS or Dt-PVNS]), a rare proliferative disease affecting large joints, vividly demonstrates the effects of deregulated CSF-1 production. In the majority of Dt-GCT patients, chromosomal translocations involving the gene encoding CSF-1 result in overexpression of this cytokine by cells within the synovial lining (West et al., 2006). This leads to massive recruitment of CSF-1R-expressing cells, mainly nonmalignant mononuclear and multinucleated cells that form the bulk tumorous mass (Cupp et al., 2007, West et al., 2006). Marginal excision or complete synovectomy remain the treatments of choice (Ravi et al., 2011) for Dt-GCT, but the disorder sometimes necessitates mutilating surgery due to locally destructive and recurring tumor growth. Another investigational approach for treating Dt-GCT patients exploits the CSF-1R-targeting component of the tyrosine kinase inhibitor imatinib mesylate (Gleevec), thus suggesting that this receptor represents an attractive target for development of cancer therapies (Cassier et al., 2012, Blay et al., 2008).